FINDING EMITTED RADIATION
AND WAVELENGTH OF MAXIMUM EMISSION
 
METEOROLOGIST JEFF HABY
All objects emit radiation. All objects also emit a variety of wavelengths of radiation. However, the
temperature of the object determines the most common range of wavelengths emitted.
The radiation emitted from an object can be expressed as the Energy emitted per unit time (Power) through an
area of the object. The metric units for this expression are Watts per meter squared (W/m^2). The equation
that relates emitted Watts per area to the temperature of the object is:
Emission = T^4 * StefanBoltzmann constant
T^4 = Temperature in Kelvins to the fourth power
StefanBoltzmann constant = 0.0000000567 Wm^2K^4
For example, the sun has a surface temperature of about 6,000 K. Find the emission from the sun
Emission = 6,000^4 K^4 * 0.0000000567 Wm^2K^4
Emission = 6,000 * 6,000 * 6,000 * 6,0000 K^4 * 0.0000000567 Wm^2K^4 = 73,483,200 Wm^2
The equation that relates the wavelength of maximum emission to the temperature of the object is:
Wavelength of max emission (um) = 2897 umK / Temperature
um = micron, which is a millionth of a meter ( 0.000001 m or can be written 10^6 meters)
2897 umK = constant that relates max emission to Temperature
Temperature = Kelvins
Although energy will be emitted in a variety of wavelengths this equation finds what the most
common emitted wavelength is. The relationship between temperature and wavelength is that as
temperature goes up the wavelength gets shorter and as the temperature goes down the wavelength
gets longer. Thus, warmer objects emit shorter wavelengths and colder objects emit longer wavelengths.
For example, what is the wavelength of maximum emission for the sun?
Wavelength of max emission (um) = 2897 umK / 6,000 K
Wavelength of max emission (um) = 0.48 um


